Pay With Credit Card Not Working

I'm getting very frustrated with trying to get my site running properly again.
I had to have new SSL certificates installed which I've done but ever since I've had problems - and more importantly my customers - with the checkout.

Everything works fine until a client tries to pay with credit card (so far this seems to be the only payment option issue) but at various places during the process I get - see attached screen capture - a warning/Parse error.

In the CHECKOUT & PAYMENT OPTIONS section various options have a warning (Square for example) that I am using PHP 5.2.17. I called the hosting company and have upgraded to 5.6 but I'm still getting the same warning.

My main question is how much would you charge to go into my site and just fix everything. This has been an on going issue for weeks and it seems that as I fix one thing something else has issues.
I've also attached a 2nd screen capture to show the other message that keeps showing up. "Test mode on. No payments will be processed."

I love Sytist but lately it has been driving me batty! Also my customers are getting frustrated that they can not place orders and I fear I am losing sales.
Any help would be great.
Thank you
John

Next issue - I'm trying to upload the screen captures for the above message and it keeps popping up that Only JPG, PNG & GIF files can be uploaded. I've tried several times to upload both JPGs and PNGs but nothing happens.
Thoughts?

Ok The PHP warning seems to be fixed but again when trying to go through Payment with credit card I am getting the message

Sorry, but your transaction was not successful. Try again if you believe this was in error. If you continue to have problems, please contact use with the following response: Response: (The merchant login ID or password is invalid or the account is inactive.)

I am using Authorize.net (AIM) as suggested in another persons question and everything else seems to be ACTIVE etc.

It probably took a little while for the PHP change to 5.6 to take effect.

1) In Settings -> Checkout & Payment, be sure " Check this box if you have an SSL installed. " is checked and Fixed SSL link is blank.

2) The authorize.net message "The merchant login ID or password is invalid or the account is inactive." basically means it is the wrong login ID or transaction key ... or your authorize.net account isn't activated.

You may be using the wrong authorize.net log in ID. It's not the login ID you use to log into authorize.net. It's the API login ID/ username which is different.

How to get your Authorize.net API username and transaction key
Log into your Authorize.net account.
In the left menu under "Account" select "Settings".
Under Security Settings, select "API Login ID and Transaction Key". This page will show you your API Login ID (which is different from your account login name). Under Create New Transaction Key, enter in your secret answer and create a transaction key.

3) If you are sure your authorize.net account is active and you are using the correct login ID and transaction key, some people have reported having failures in test mode (I haven't had those issues). So if you have the payment option in test mode, remove the test mode option and try a live transaction.